Synthesis of a Fluorescent Analogue of Paclitaxel that Selectively Binds Microtubules and Sensitively Detects Efflux by P‐Glycoprotein

The anticancer drug paclitaxel (Taxol) exhibits paradoxical and poorly understood effects against slow-growing tumors. To investigate its biological activity, fluorophores such as Oregon Green have been linked to this drug. However, this modification increases its polarity by approximately 1000-fold and reduces the toxicity of Taxol towards cancer cell lines by over 200-fold. To construct more drug-like fluorescent probes suitable for imaging by confocal microscopy and analysis by flow cytometry, we synthesized derivatives of Taxol linked to the drug-like fluorophore Pacific Blue (PB). We found that PB-Gly-Taxol bound the target protein β-tubulin with both high affinity in vitro and high specificity in living cells, exhibited substantial cytotoxicity towards HeLa cells, and was a highly sensitive substrate of the multidrug resistance transporter P-glycoprotein (P-gp).